Power IC (Integrated Circuit; semiconductor integrated circuit) devices have been evolving for power management and power control through integration with high current/high voltage compatible power MOS (Metal Oxide Semiconductor) transistors and their control circuits.
Some essential properties of the power IC device include low manufacturing cost, low ON resistance, and high operation speed. Low ON resistance is required in order to achieve low voltage drop when the power IC device is used, for example, in a high drive circuit which allows only for extremely low ON voltage drop.
Accordingly, patent document 1 discloses, as illustrated in FIG. 10, a power IC device structure integrating a DMOS (Double Diffused Metal Oxide Semiconductor) transistor as a power MOS transistor and a surface channel MOS transistor as a control circuit for the DMOS transistor. The surface channel MOS transistor has a structure including wells, sources and drains, a gate insulating film, and gates which are sequentially formed in the surface layer of a chip and is fabricable by general MOS transistor fabrication technology.
The power MOS transistor in the power IC device needs to be a p-channel power MOS transistor to achieve low manufacturing cost, one of the listed requirements, for the following reasons. The n-channel power MOS transistor needs an overdrive circuit supplying higher gate voltage than power supply voltage when connected (gate step-up circuit). On the other hand, the p-channel power MOS transistor needs no gate step-up circuit.
Patent Document 1: U.S. Pat. No. 4,795,716, Specification (Jan. 3, 1989)
Patent Document 2: Japanese Unexamined Patent Publication No. 2004-356114 (Tokukai 2004-356114; published Dec. 16, 2004)
Patent Document 3: Japanese Unexamined Patent Publication No. 2004-200672 (Tokukai 2004-200672; published Jul. 15, 2004)
Non-patent Document 1: Roughening of Single-Crystal Silicon Surface etched by KOH Water Solution, K. Sato et al, Sensors and Actuators, A PHYSICAL, U.K., U.S., ELSEVIER, 1999, Vol. 73, pp. 122-130